Photoflash lamp



Dec. 11, 1962 F. ANDERSON EI'AL 3,

PHOTOFLASH LAMP Original Filed Oct. 21, 1957 Fly 2 'zoossc.

MEGALUMENS M ILLISECONDS LESTER F ANDERSON WILLIAM C. FINK INVENTORSATTORNE United States Patent Ofifice 3,067,601 Patented Dec. 11, 19623,067,601 PHOTOFLASH LAMP Lester F. Anderson and William C. Fink,Williamsport,

Pa., .assignors to Sylvania Electric Products Inc., a

corporation of Delaware Continuation of application Ser. No. 691,298,Oct. 21,

1957; This application Sept. 29, 1960, Ser. No. 59,358

12 Claims. (Cl. 67--31) This invention relates to photofiash lamps andmore particularly to photofiash lamps in which zirconium is employed asthe combustible.

In the manufacture of photofiash lamps, it has been the generalcommercial practice in recent years to employ aluminum foil shredded tofilamentary form as the combustible and oxygen as thecombustion-supporting gas, with the ratio between combustible and weightof gas maintained at or near stoichiometric balance. The lamp envelopeis provided with an external, and, on large lamps, an internal coatingas a safety precaution to prevent fragmentation, since the pressureduring combustion rises to values many times initial pressure becausethe heat developed expands the oxygen gas. Over the years, increases inthe total light output per unit volume of the lamp envelope have beenmade possible by the use of stronger lamp envelopes, stronger coatings,and improved techniques in the dispersion and distribution of thefilamentary combustible in the lamp envelope.

Concurrently with the efforts to achieve higher levels of light outputper unit volume has been an attempt to develop photofiash lamps having acolor temperature that would be equivalent to daylight in order to giveperfect balance when used with daylight color film. The colortemperature of the aluminum-oxygen reaction is approximately 380.0 K.Since the color temperature of daylight plus skylight, for whichdaylight color film is balanced, is about 6000 K., it has been the usualpractice to introduce a blue dye into the exterior lacquer coating onthe lamp envelope to act as a filter, thus effectively raising the colortemperature from about 3800" K. to about 6000" K. Absorption of light bythe filter coating on an aluminum-filled lamp is about 55%.

Although, as pointed out above, increases in the total light output perunit volume of the lamp envelope of an aluminum-filled photofiash lamphave been obtained by the use of stronger lamp envelopes and/ orstronger coatings, we have found that when zirconium foil, preferablyreactor grade, shredded to filamentary form, is employed as thecombustible, a substantial increase in the total light output per unitvolume of the lamp envelope is obtainable without the necessity forusing stronger lamp envelopes and/ or stronger coatings. We have alsofound that the color temperature of a photofiash lamp provided with acombustible of filamentary zirconium is approximately 300" K. higherthan the color temperature of a photofiash lamp provided with acombustible of filamentary aluminum, thus making it possible to reducethe absorption of the blue filter coating employed to raise the colortemperature to about 6000 K.

Other advantages and features of the photofiash lamp of our inventionwill be pointed out in connection with the description of theaccompanying drawings in which:

FiGURE l is a plot of light output in terms of megalumens against timein terms of milliseconds.

FIGURE 2 is a plot of various camera shutter speeds.

FIGURE 3 is an elevational view partly in section of a photofiash lamp.

Curve A in FIGURE 1 illustrated the light output characteristic ofphotofiash lamps known in the trade as M2s. The M2 lamps used in thistest were provided with about 15 milligrams of aluminum foil shredded tofilamentary form as the combustible and oxygen at about cms. Hg, as thecombustion-supporting gas, with the ratio between combustible and weightof gas at or near stoichiometric balance. The lamp envelope employed wasa T6/: bulb having a cubical content of about 7.5 cc.

Curve B in FIGURE 1 illustrates the light output characeristic ofphotofiash lamps provided with about 48 milligrams of zirconium foilshredded to filamentary form as the combustible and oxygen at about 130cms. Hg, as the combustion-supporting gas, with the ratio betweencombustible and weight of gas at or near stoichiometric balance. Thelamp envelope employed was a T6 /2 bulb having a cubical content ofabout 7.5 cc.

Curve C in FIGURE 1 illustrates the light output characteristic ofphotofiash lamps known in the trade as Press 25 's. The Press 25 lampsused in this test were provided with about 33 milligrams of aluminumfoil shredded to filamentary form as the combustible and oxygen at about53 cms. Hg, as the combustion-supporting gas, with the ratio betweencombustible and weight of gas at or near stoichiometric balance. Thelamp envelope employed was a B12 bulb having a cubical content of about31 cc.

The filamentary aluminum used as the combustible in the M2 lamps and thePress 25 lamps had cross sections of about 0.4 10 and 0.65 10 sq. in.respectively. The cross section of the filamentary zirconium used in thelamps of Curve B was about 1.2 l0- sq. in.; however, satisfactoryresults may be obtained with cross sections between about O.4 10- toabout 1.8 10 sq. in.

The lamp envelopes used in the manufacture of the amps of Curves A andC, as well as the aluminum fill, oxygen pressure and other structuralcharacteristics, are identical to those presently employed in thecommercial manufacture of M2s and Press 25s. The initial gas fillpressures with which these lamps were provided were determined primarilyby safety considerations. The instantaneous peak pressures on firing ofthese lamps are as close to the maximum pressures, which the lampenvelopes can withstand without danger of explosion, as is practical andstill provide a reasonable factor of safety.

Turning now to FIGURE 1, it will be noted that Curve B, representing thezirconium lamp, is flatter than either Curve A or Curve C, representingthe present commercial, filamentary aluminum-filled M2 and Press 25respectively. Apparently, for the cross sections selected, the zirconiumignites very rapidly but radiates useful energy for a longer timecompared to aluminum. These combined characteristics enhance theadaptability of the zirconium lamp for use with both high speedsynchronization in the more expensive cameras and the relatively slowspeed synchronization of the fixed focus box camera.

Camera shutter speeds of sec., sec., sec., and box camera speed areillustrated schematically in FIGURE 2. In order to determine the lightoutput that camera film will actually see, it is necessary to integratethat portion of each of the curves in FIGURE 1 for which the shutter isopen. It will be noted that the peak of Curve A, the M2 lamps, occursseveral milliseconds ahead of the opening of the shutter of the highspeed camera, and, therefore, M2 lamps cannot be used for high speedsynchronization at all. The M2 is designed to peak early in order togive maximum light output for box cameras. its peak characteristic istoo sharp and total light output too low to attempt to design the lampfor satisfactory synchronization on both high speed and box cameras.

Total integration of the lamps illustrated gives about 7200 lumenseconds for the M2 lamps, about 20,000 lumen seconds for the Press 25lamps, and about 18,000 lumen seconds for the zirconium lamps.

For high speed synchronization, the following useful light outputs areobtained:

For the fixed focus box camera, assuming second Opening, the followinguseful light outputs are obtained:

Lamp: Lumen seconds M2 7,000 Press 25 12,000 Zirconium 13,000

Thus it can be seen that, at high speed synchronization, the smallzirconium lamp is virtually the equivalent of the aluminum-filled Press25. Since, as was noted above, the cubical content of the zirconium lampused was about 7.5 cc., and the cubical content of the Press 25 lampused was about 31 cc., the zirconium lamp gives substantially the samelight output with one fourth the envelope volume.

As was mentioned above, the color temperature of the aluminum-oxygenreaction is about 3800 K., and a blue dye is usually introduced into thelacquer coating on the lamp envelope to act as a filter and thuseffectively raise the color temperature to about 6000 K. Since the colortemperature of the zirconium lamp is about 300 K. higher than thealuminum lamp, the absorption of the blue filter may be reduced, andthus make it possible to obtain a daylight rating of 9,000 lumen secondsfor a zirconium-filled lamp in a lamp envelope of about 7.5 cc. volume,compared to a daylight rating of 8,000 lumen seconds for analuminum-filled lamp in a lamp envelope of about 31 cc. volume. Whenpressures substantially higher than those mentioned in the descriptionof FIG- URE 1 are used, lamp envelopes capable of withstanding the shockof very high instantaneous peak pressures on firing, such as thosedescribed in the co-pending application of Anderson et al., Serial No.516,722, filed June 20, 1955, now US. Patent 2,865,186, should beemployed.

It is possible to make a zirconium flash lamp as illustrated in FIGURE 1because of the greater efficiency of combustion of zirconium compared toaluminum, and because of the lower peak instantaneous pressure that isdeveloped in the zirconium lamp. For comparable envelopes using the sameprotective coatings, the zirconium lamp will remain intact uponflashing, where initial pressures are substantially higher than thosefor aluminum. In all these cases, the charge is in susbtantialstoichiometric balance. Peak pressures for comparable zirconium andaluminum lamps in the same type envelopes have been measured on apressure transducer. At constant initial pressure, the instantaneouspeak pressures developed in the aluminum lamps range from about 28%higher to as much as about 100% higher compared to zirconium lamps.Instantaneous peak pressures are approximately equal, viz., about 250cms., for the com mercial M2 lamp having an initial pressure of about 95cms. and the zirconium lamp, whose characteristic is illustrated inFIGURE 1, Curve B, having an initial pressure of about 130 cms. Thus thezirconium lamp is provided -with a gas filling at a pressure more thanone-half of the pressure which the envelope can withstand safely uponfiring whereas the gas filling with which the aluminum lamp is providedis at a pressure substantially less than one-half of the pressure whichthe envelope can withstand safely upon firing. The ratio ofinstantaneous peak pressure to initial fill pressure for the aluminumfilled M2 lamp is about 2.6 to 1 whereas for the zirconium filled lampit is only about 1.9 to 1. As the initial pressureis increase.

increased, the difference in instantaneous peak pressures between thetwo types of combustible also appears to This is a significant advantagein view of the fact that, up to certain high pressure regions,efliciency increases with increases in gas pressures, because it makespossible the use of higher initial pressures with less danger offragmentation of the lamp envelope.

In addition to the features and advantages described above whichcharacterize a photofiash lamp employing filamentary zirconium as thecombustible, we have noted that faster and more reliable ignition maybeobtained from the low power battery sources used because the zirconiumrequires lower activation energy than aluminum and therefore can beignited at lower temperatures. Although the problem of inadvertentignition ofa photoflash lamp is always one to be reckoned with, we havealso noted that filamentary zirconium is characterized by betterconductivity compared to filamentary aluminum, which is always slightlyoxidized. This makes possible more positive internal grounding and thusreduces susceptibility to ignition by static discharges or dischargesoccurring in a dynamic field such as radar.

Referring now to FIGURE 3, the photofiash lamp shown therein is, exceptfor the combustible described above, a conventional, commercialphotofiash lamp and thus will be described only briefly. It comprises ahermetically sealed, glass, light-transmitting envelope 2 provided witha filling of gas, such as oxygen, and filamentary zirconium. Theenvelope 2 is provided with a base 6 affixed to the neck thereof. Atungsten filament 8, the ends of which are attached to lead-in wires 10and 12 is disposed within envelope 2. The inner ends of the lead-inwires 10 and 12 are provided with a quantity of ignition paste 14. Thelead-in wires 10 and 12 are supported within envelope 2 by stem 16 andare connected to conventional base contacts in the usual manner. Theouter wall of the lamp envelope is provided with a protective coating 18to prevent fragmentation during firing of the lamp.

This application is a continuation of our co-pending application, SerialNumber 691,298, filed October 21, 1957, entitled Photoflash Lamp, nowabandoned.

What we claim is:

1. A photofiash lamp comprising: a sealed light-transmitting envelope; acombustion-supporting gas filling in said envelope at a pressure aboveatmospheric, the quantity of said gas being at least about 2 mgs. percc. of envelope volume; a quantity of filamentary zirconium disposed insaid envelope; and ignition means disposed in said envelope in operativerelationship with respect to said filamentary zirconium.

2. A photofiash lamp comprising: a sealed light-transmitting envelope;an oxygen gas filling in said envelope at a pressure above atmospheric,the quantity of said gas being at least about 2 mgs. per cc. of envelopevolume; a quantity of filamentary zirconium disposed in said envelope;and ignition means disposed in said envelope in operative relationshipwith respect to said filamentary zirconium.

3. A photofiash lamp comprising: a sealed light-transmitting envelope;an oxygen gas filling in said envelope at a pressure above atmospheric,the quantity of said gas being at least about 2 mgs. per cc. of envelopevolume; a quantity of filamentary zirconium, having a cross-section ofbetween about 0.4 10- sq. in., to about 1.8)(10 sq. in., disposed insaid envelope, the ratio between said filamentary zirconium and theweight of said gas being substantially in stoichiometric balance; andignition means disposed in said envelope in operative relationship withrespect to said filamentary zirconium.

4. A photofiash lamp comprising: a sealed light-trans mitting envelope;a combustion-supporting gas filling in said envelope at a pressure aboveatmospheric; a quantity of filamentary zirconium, having a cross-sectionof between about 0.4)(10 sq. in., to about 1.8 10- sq.

in., disposed in said envelope, the ratio between said filamentaryzirconium and the Weight of said gas being substantially instoichiometric balance; and ignition means disposed in said envelope inoperative relationship with respect to said filamentary zirconium, saidlamp producing a total light output of about 1000 lumen seconds per mg.of the combustion-supporting gas.

5. A photoflash lamp comprising: a sealed light-transmitting envelope; acombustion-supporting gas filling in said envelope at a pressure aboveatmospheric, the quantity of sai gas being at least about 2 mgs. percc., of envelope volume; a quantity of filamentary zirconium disposed insaid envelope; and ignition means disposed in said envelope and inoperative relationship with respect to said filamentary zirconium, saidlamp producing a total light output of about 1000 lumen seconds per mg.of the combustion-supporting gas.

6. A photo-flash lamp comprising: a sealed light transmitting envelope;a combustion-supporting gas filling in said envelope at a pressure aboveatmospheric, the quantity of said gas being at least about 2 tags. percc. of envelope volume; a quantity of filamentary zirconium, having across-section of between about 0. l l0 sq. in., to about 1.8x sq. in.,disposed in said envelope, the ration between said filamentary zirconiumand the weight of said gas being substantially in stoichiometricbalance; and ignition means disposed in said envelope and in operativerelationship with respect to said filamentary zirconium, said lampproducing a total light output of about 1000 lumen seconds per mg. ofthe combustionsupporting gas and a total light output per unit envelopevolume of at least about 2000 lumen seconds per cc.

7. A photoflash lamp comprising: a sealed light-transmitting envelope;an oxygen gas filling in said envelope at a pressure above atmospheric,the quantity of said gas being at least about 2 mgs. per cc. of envelopevolume; a quantity of filamentary zirconium, having a cross-section ofbetween about 0.4)(10 sq. in., to about 1.8 l0 sq. in., disposed in saidenvelope, the ratio between said filamentary zirconium and the weight ofsaid gas being substantially in stoichiometric balance; and ignitionmeans disposed in said envelope and in operative relationship withrespect to said filamentary zirconium, said lamp producing a total lightoutput of about 1000 lumen seconds per mg. of the oxygen gas and a totallight output per unit envelope volume of at least about 2000 lumenseconds per cc.

8. A photoflash lamp comprising: a sealed light-transmitting envelope ofglass; a combustion-supporting gas filling in said envelope, the initialfill pressure being above atmospheric and the ratio of instantaneouspeak pressure to initial fill pressure being less than 2 to l; aquantity of filamentary zirconium disposed in said envelope; andignition means disposed in said envelope in operative relationship withrespect to said filamentary zirconium.

9. A photoflash lamp comprising: a sealed ight-transmitting envelope orglass; an oxygen gas lilling in said envelope at a pressure aboveatmospheric and at least one half of the pressure which said envelopecan withstand safely upon firing; a quantity of filamentary zirconiumdisposed in said envelope; and ignition means disposed in said envelopein operative reiationship with respect to said filamentary zirconium.

10. A photoflash lamp comprising: a sealed light-transmitting envelope;an oxygen gas filling in said envelope, the initial fill pressure beingabove atmospheric and the ratio oi instantaneous peak pressure toinitial'fill pressure being less than about 2 to 1; a quantity offilamentary zirconium disposed in said envelope; and ignition meansdisposed in said envelope and in operative relationship with respect tosaid filamentary zirconium.

l l. A photoflash lamp comprising: a sealed light-transmitting envelope;at combustion-supporting gas filling in said envelope at a pressureabove atmospheric and at least one-half of the pressure which said.envelope can Withstand salely upon firing; a quantity of filamentaryzirconium disposed in said envelope; and ignition means disposed in saidenvelope and in operative relationship with respect to said filamentaryzirconium.

12. A photoflash lamp comprising: a sealed light-transmitting envelope;at combustion-supporting ga filling in References Cited in the file ofthis patent UNITED STATES PATENTS Re. 18,678 Ostermeir Dec. 6, 19322,272,059 De Margitta Feb. 3, 1942 2,272,779 Sarbey Feb. 10, 19422,315,099 Van Liempt Mar. 20, 1943 2,810,283 Cohen et a1 Oct. 22, 19572,813,411 Johnson Nov. 19, 1957 2,865,186 Anderson et al. Dec. 23. 1958

1. A PHOTOFLASH LAMP COMPRISING: A SEALED LIGHT-TRANSMITTING ENVELOPE; ACOMBUSTIION-SUPPORTING GAS FILLING IN SAID ENVELOPE AT A PRESSURE ABOVEATMOSPHERIC, THE QUANTITY OF SAID GAS BEING AT LEAST ABOUT 2 MGS. PERCC. OF EN-